RoR course: RSS Maker/Parser

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I would like to share the details of how Ruby supports to generate and read the RSS. Before going into details, let us look into few basics of what we are going to deal with.

There will be very few and hardly few people in this web world who does not know about the RSS/Feeds. To keep things simple and elegant:

Note: An RSS document is often referred as “feed” or “web feed” or “channel”.

What is RSS?

• Really Simple Syndication.
• It is a easy way to share defined content and news/titles/posts from www
• RSS is written in XML

Why use RSS?

RSS can be updated automatically; this enables users to track/monitor their favorite sites, news channels, websites… without even going/visiting the sites. Since it is simple, light and fast-loading this can be used even in PDA’s, mobiles thus ensuring the accessibility even simpler.

Who should use RSS?

RSS is ideal to be used if the source is dynamic. In the sense that would change rapidly for say new sites, micro/web blogs… RSS is not meant for static pages, website that doesn’t have updates frequently.

Well the next obvious question would be How do I read them?

With so many websites/blogs/calendars… everybody generating the RSS, the reading/grabbing job is taken care by “RSS/feed reader” or “aggregator”. These aggregators can be either desktop based or web based. The user needs to subscribe his favorite site feeds by submitting the RSS link provided by the site to these aggregators and they would send the user the subscribed updates as and when they occur.

Having answered the few basic “W’s”, it would make perfect sense for us to plunge into RSS implementation of the same in Ruby on Rails.

Ruby excellently supports the RSS implementations. RSS (v0.9, v1.0, v2.0), maker and parser. Moving ahead here I will be showing few examples how do we parse/generate the RSS feeds in Rails application.

Note: An RSS document is often referred as “feed” or “web feed” or “channel”.

Parser:

Parser identifies the feed Url provided and reads the document and we can publish the feed with our own display options. So all that we need is a simple feed url. Let us say we need to publish the feed content of particular site on our blog/site.

Since there are multiple versions of the RSS available based on the version we need to include/require those libraries while parsing the feed.

1. A controller that would handle all the feed related actions, includes/refers the required libraries.
2. An action/method that would use the rss/parser library to read the feed.
3. Extract the necessary elements/content.
4. Pass on the elements/content to the views.

require 'open-uri'

require 'rss/0.9'

require 'rss/1.0'

require 'rss/2.0'

require 'rss/parser'

require "rexml/document"

class RssFeedController <>

#This action is used to get the rss feed of the blog mentioned

def parse_feed

url = 'feed url'

rss = RSS::Parser.parse(open(url){|fd|fd.read})

item_rss=rss.items.collect{|item|item.title}

item_link=rss.items.collect{|item|item.link}

@p=item_rss.length

@postfeed=item_rss

@postlink=item_link

@link="url of the link"

return @postfeed,@postlink,@p,@link

end

end

The view part will be a list of articles/content displayed looping over the length of feed.

<%@postlength.times do|i|%>

<li>

<a class="define style" target="_blank" href="<%=@postlink[i]%>">

<%=@postfeed[i]%>

a>

li>

<%end%>

Thus we are done with parsing or reading the existing feed or RSS document.

The view part will be a list of articles/content displayed looping over the length of feed.

Maker:

Maker creates/generates the feed/RSS document of a site/blog. Since there are multiple versions of the RSS available based on the version we need to include/require those libraries while making the feed.

1. A controller that would handle all the feed related actions, includes/refers the required libraries.
2. An action/method that would use the rss/maker library to read the feed.
3. Extract the necessary elements/content.
4. Pass on the elements/content to the views (RHTML/RXML).

def generate_feed

version = "2.0"

content = RSS::Maker.make(version) do |m|

m.channel.title = "Title of the post/entry"

m.channel.link = "http://www.linktopost.com"

m.channel.description = "Describe the post"

i = m.items.new_item

i.title = "Ruby to generate RSS feeds"

i.link = "http://www.linktopost.com"

i.description = "Describe the post"

i.date = Time.now

end

end

As you find the above two actions were created for RSS 2.0, hence we have the elements as title, link, description, date… which are as pert RSS 2.0. Based on the version we are referring/using they would change accordingly.

This is a static content based on which we created the feed, to create a dynamic feed say for the posts, articles should iterate over them and pass the info accordingly.

In nutshell, Ruby provides the RSS support with

RSS::Maker.make

RSS::Parser.parse

There are umpteen number of rails plug ins were created and available for rails community that were built on the above mentioned core ruby classes.

Feed Fetcher

Feed Tools

Resource Feeder

Atom Feed helper

…

…

…

This document is prepared as part of Ruby on Rails course that I am writing in blog TechSavvy.

Have something to discuss/suggest/enhance: Reach me tosumanthkrishna (gmail)

References:

http://en.wikipedia.org/wiki/RSS

http://www.w3schools.com/default.asp

http://www.rubyrss.com/

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